This invention relates to position sensors and, more particularly, in a lid latched at a pair of side edges and revolving about a horizontal axis of rotation between open, closed and unlatched, and closed and latched positions wherein the closed and unlatched and closed and latched positions are rotationally displaced from one another, to a method of determining the status of both of a pair of latches releasably latching the lid without physically sensing either of the pair of latches. The method comprises the steps of, providing a pair of reflectors carried by one of the lid and the cabinet adjacent respective ones of the pair of latches; providing a pair of non-contacting optical sensors each including a light detector carried by another of the lid and the cabinet adjacent respective ones of the pair of latches for directing a beam of light from an emitter thereof; positioning each of the pair of reflectors and the pair of non-contacting optical sensors such that the beam of light strikes the reflector to be reflected thereby at an input surface of the light detector when the lid adjacent an associated latch is in a closed and latched position and the beam of light does not strike the reflector to be reflected thereby at the input surface of the light detector when the lid adjacent the associated latch is in a closed and unlatched position; emitting the beam of light from the emitter of the optical sensors; receiving the beam of light if reflected by the reflector at the input surface of the light detectors; and, outputting electrical signals as a function of light striking the input surfaces whereby the status of the latches is directly related to the electrical signals.
Cabinets with doors and lids are used in various environments. A cabinet 10 with a lid 12 is depicted in simplified form in FIG. 1. As is typical in such cases, the lid 12 moves between an open position (shown ghosted) and a closed position. The position of the lid 12 can be sensed reliably with a sensor 14 having a spring-loaded plunger 16 since the lid 12 is either open or closed. The position of the plunger 16 (extended or retracted) is output on the wires 18. Thus, the wires 18 can be connected to be sensed by a control circuit, light a warning light, or whatever is needed under the circumstances. When the lid 12 is lifted to the open position, the plunger 16 extends and an open condition is indicated by the sensor 14. When the lid 12 is lowered to the closed position, it compresses the plunger 16 and a closed condition is indicated by the sensor 14. If a friction or magnetic catch is employed to hold the lid 12 in the closed position, it does not affect the sensor 14.
In a wide lid or the like, two latches may be employed with one at each side. A sensor such as sensor 14 cannot detect when one side of the lid is closed and latched and the other is closed and slightly ajar, i.e. not latched.
In some instances, however, a lid or door cannot be securely held in a closed position with a friction or magnetic catch since such devices will release upon sufficient opening force being applied. Typically, the opening force required to release a friction or magnetic catch is quite small. Where a lid or door must be securely held in a closed position and it is still desired to be able to open and close the lid or door securely, a push-to-release latch is employed. As depicted in FIG. 2, a push-to-release latch has two stable closed positions. One position (in which the lid 12 is shown ghosted) is where the lid 12 is closed but not latched. The other (non-ghosted lid 12) is where the lid 12 is both closed and latched. The operation of such latches is well known to those skilled in the art and they do not form any part of the present invention; so, the push-to-release latch is not depicted in the drawings for simplicity. To close and latch a push-to-release latch, the lid 12 is moved to the ghosted position of FIG. 2. The lid 12 is then pushed more firmly towards the closed position against a bias force of the push-to-release latch. In latching, the lid 12 actually passes to an overtravel position (shown in FIG. 4) causing the latch within the push-to-release latch to engage. When the closing pressure on the lid 12 is released, the lid 12 moves to the non-ghosted position of FIG. 2 where it is closed and latched. To release the push-to-release latch so that the lid 12 can be opened, the lid 12 is again pushed firmly towards the closed position against the bias force of the push-to-release latch until it reaches the overtravel position, at which the latch within the push-to-release latch disengages. When the pressure on the lid 12 is released, the lid 12 moves to the ghosted position of FIG. 2 where it is closed and unlatched. It can then be raised to its open position. A door operating with a push-to-release latch operates in the same manner except that the motion of the door is about a vertical axis of rotation while a lid moves about a horizontal axis of rotation.
The above-mentioned condition of the lid 12 being closed and latched on one side and being closed and slightly ajar, i.e. not latched, on the other side as depicted in FIG. 5 is a high probability situation when push-to-release latches, or the like, are employed as merely lowering the lid 12 will not result in both latches latching.
If it necessary that a particular lid or door be closed and latched with certainty, the prior art approach of FIG. 1 will not work as depicted in FIG. 2. Whether the lid 12 (or one or both sides thereof) is in its closed and latched or its closed and unlatched position, the plunger 16 is depressed and the same signal appears on the wires 18. A mechanical finger or microswitch can sometimes be employed; but, because of the overtravel of the lid 12 in latching and unlatching, such an approach is not reliable and prone to problems of adjustment, mis-adjustment, and going out of adjustment.
A plotter as to be commercially produced by the assignee of this application is such a case in point. Appearing substantially like the simplified drawing of FIG. 5, if both sides of an elongated lid structure are not completely closed and latched prior to operation, paper skew can take place causing mis-operation of certain functions. To try to sense the status of the latches latching the two sides of the lid structure employing any mechanical means can greatly reduce the reliability and mean time between failures of the plotter.
Wherefore, it is an object of this invention to provide a sensing system for doors, lids, and such, latched by push-to-release latches, or the like, which is simple to install and adjust and which is reliable in operation and not prone to going out of adjustment.
It is another object of this invention to provide a way of sensing the status of multiple latches holding doors, lids, and such, shut without physically contacting the latch itself.
It is yet another object of this invention to provide a way of determining the status of a latch without physically contacting the latch itself by sensing the status of a member held by the latch.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.